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--My son has no enough money to support me. He will file his I-864 by himself to "sponser" me.

"But he still needs to file I-864, and you file I-864A to use your income together."

--Do you mean I can fill out and file I-864A to sponser myself?

-You may use your income in US to support yourself by filing I-864A. Read I-864A and I-864 Instructions carefully.

If you don't understand it well, you had better consult an immigrant lawyer.

--Do I still need to ask my friend (a US citizen in CA) to file her I-864A to sponser me, considering my permanetn employment status (subjec to 3 years renewal of TN as of now) with employer provided health insurance, income well above proverty line, US College degrees, professional certiifcates and skills, and 800+ credit score?

-It the better way to ask your friend to file another I-864 (not I-864A) for you as the joint sponsor if she agrees to do that. Thus, you don't need to file I-864A. 

多謝8老師!!!